The present invention relates to indicator devices that display information about the extent of remaining useful life of associated products. These indicator devices are particularly well suited for use with air treatment chemical dispensers.
Many products have a useable life dependent upon the time the product is exposed to a surrounding environment and/or operated. For example, a variety of products are designed to dispense air treatment chemicals from an impregnated substrate. Sometimes the evaporation is assisted by heating the substrate. Other times it is assisted by having a fan or other device blow air across the substrate. In still other cases the air treatment chemical can volatize even without the assistance of heating or blown air (e.g. passive evaporation).
Unfortunately, such evaporation typically will not alter the visible appearance of the substrate. Moreover, even if it did, these substrates are sometimes housed internally within such devices where they cannot be easily visually monitored. This makes it difficult to know when the substrate is near the end of its useful life.
In a variety of other contexts it is similarly valuable to be able to monitor the status of products where the product itself does not accurately visually disclose that information. For example, food products will often degrade over time. While many food products will exhibit this degradation in a visually perceptible manner, for some the freshness will not be evident from visible changes in the product itself.
A variety of methods and devices have been developed to alert consumers as to the status of products. For example, packaging for some products includes a date stamp indicating the estimated end of the useable product life. However, consumers may not read or remember that information. Further, given the wide range of conditions to which such products may be exposed, suggested useful life information may not be accurate in many cases. This can lead to use of the product after its effective useful life (with resulting consumer dissatisfaction). Alternatively, it can lead to premature disposal of a still useful product (and thus unnecessary cost and waste).
A wide variety of gauges and other devices have been developed to provided use-up/useful life information. See generally U.S. Pat. Nos. 2,923,157, 3,417,730, 4,921,636, 5,923,648, 5,385,044, 5,388,331, and 5,538,161. See also U.S. Pat. No. 4,824,917 (evaporation of a solvent leads to a color change); and U.S. Pat. No. 6,790,670 (evaporation of a dye leads to a color change). See also S.C. Johnson & Son's U.S. Ser. No. 11/346,697 filed on Feb. 3, 2006 (volatile indicator material held separately from volatile air treatment chemical, but with rates of volatilization coordinated).
While these devices do provide improved monitoring of the product status, the inexpensive ones are typically designed to identify the final use-up point, rather than displaying information about the degree of use-up. In this regard, it is one thing to have an indicator that displays a warning near or at the use-up point. It is another to also be able to have more specific indications about the extent of partial use, particularly where this can be achieved at low cost.
Thus, a need exists for improved automatic useful life indicators, particularly where such indicators are capable of providing detailed information about the state of partial use-up without requiring complex or expensive structures to achieve this advantage.